Google Maps API v3: How do I dynamically change the marker icon?

Call the marker.setIcon('newImage.png')... Look here for the docs.

Are you asking about the actual way to do it? You could just create each div, and a add a mouseover and mouseout listener that would change the icon and back for the markers.

You can also use a circle as a marker icon, for example:

var oMarker = new google.maps.Marker({
    position: latLng,
    sName: "Marker Name",
    map: map,
    icon: {
        path: google.maps.SymbolPath.CIRCLE,
        scale: 8.5,
        fillColor: "#F00",
        fillOpacity: 0.4,
        strokeWeight: 0.4
    },
});

and then, if you want to change the marker dynamically (like on mouseover), you can, for example:

oMarker.setIcon({
            path: google.maps.SymbolPath.CIRCLE,
            scale: 10,
            fillColor: "#00F",
            fillOpacity: 0.8,
            strokeWeight: 1
        })

This thread might be dead, but StyledMarker is available for API v3. Just bind the color change you want to the correct DOM event using the addDomListener() method. This example is pretty close to what you want to do. If you look at the page source, change:

google.maps.event.addDomListener(document.getElementById("changeButton"),"click",function() {
  styleIcon.set("color","#00ff00");
  styleIcon.set("text","Go");
});

to something like:

google.maps.event.addDomListener("mouseover",function() {
  styleIcon.set("color","#00ff00");
  styleIcon.set("text","Go");
});

That should be enough to get you moving along.

The Wikipedia page on DOM Events will also help you target the event that you want to capture on the client-side.

Good luck (if you still need it)

The GMaps Utility Library has a plugin called MapIconMaker that makes it easy to generate different marker styles on the fly. It uses Google Charts to draw the markers.

There's a good demo here that shows what kind of markers you can make with it.

You can try this code

    <script src="http://maps.googleapis.com/maps/api/js"></script>
<script type="text/javascript" src="http://google-maps-utility-library-v3.googlecode.com/svn/trunk/infobox/src/infobox.js"></script>

<script>

    function initialize()
    {
        var map;
        var bounds = new google.maps.LatLngBounds();
        var mapOptions = {
                            zoom: 10,
                            mapTypeId: google.maps.MapTypeId.ROADMAP    
                         };
        map = new google.maps.Map(document.getElementById("mapDiv"), mapOptions);
        var markers = [
            ['title-1', '<img style="width:100%;" src="canberra_hero_image.jpg"></img>', 51.508742, -0.120850, '<p> Hello - 1 </p>'],
            ['title-2', '<img style="width:100%;" src="canberra_hero_image.jpg"></img>', 51.508742, -0.420850, '<p> Hello - 2 </p>'],
            ['title-3', '<img style="width:100%;" src="canberra_hero_image.jpg"></img>', 51.508742, -0.720850, '<p> Hello - 3 </p>'],
            ['title-4', '<img style="width:100%;" src="canberra_hero_image.jpg"></img>', 51.508742, -1.020850, '<p> Hello - 4 </p>'],
            ['title-5', '<img style="width:100%;" src="canberra_hero_image.jpg"></img>', 51.508742, -1.320850, '<p> Hello - 5 </p>']
        ];

        var infoWindow = new google.maps.InfoWindow(), marker, i;
        var testMarker = [];
        var status = [];
        for( i = 0; i < markers.length; i++ ) 
        {
            var title = markers[i][0];
            var loan = markers[i][1];
            var lat = markers[i][2];
            var long = markers[i][3];
            var add = markers[i][4];


            var iconGreen = 'img/greenMarker.png'; //green marker
            var iconRed = 'img/redMarker.png';     //red marker

            var infoWindowContent = loan + "\n" + placeId + add;

            var position = new google.maps.LatLng(lat, long);
            bounds.extend(position);

            marker = new google.maps.Marker({
                map: map,
                title: title,
                position: position,
                icon: iconGreen
            });
            testMarker[i] = marker;
            status[i] = 1;
            google.maps.event.addListener(marker, 'click', ( function toggleBounce( i,status,testMarker) 
            {
                return function() 
                {
                    infoWindow.setContent(markers[i][1]+markers[i][4]);
                    if( status[i] === 1 )
                    {
                        testMarker[i].setIcon(iconRed);
                        status[i] = 0;

                    }
                    for( var k = 0; k <  markers.length ; k++ )
                    {
                        if(k != i)
                        {
                            testMarker[k].setIcon(iconGreen);
                            status[i] = 1;

                        }
                    }
                    infoWindow.open(map, testMarker[i]);
                }
            })( i,status,testMarker));
            map.fitBounds(bounds);
        }
        var boundsListener = google.maps.event.addListener((map), 'bounds_changed', function(event)
        {
            this.setZoom(8);
            google.maps.event.removeListener(boundsListener);
        });
    }
    google.maps.event.addDomListener(window, 'load', initialize);

</script>

<div id="mapDiv" style="width:820px; height:300px"></div>